Extraction and air/water cooling system for large quantities of heavy ashes

ABSTRACT

The present invention relates to an extraction and air/water cooling system and energy recovery for large flows of heavy ashes, produced by solid fuel boilers ( 100 ), able to reduce final temperature of the extracted ash, without increasing the air flow entering the throat of the boiler. When the air flow needed for cooling process exceeds the maximum flow admissible in the boiler, the system allows to the exceeding air and to the possible steam to be sent to the fume duct in the most appropriate point, thanks to a separation of the cooling environment made by the ash itself. The separation of the environments of the cooling system is handled automatically based upon a temperature signal of the ash at the system exhaust. If the cooling air is not sufficient to cool the ash, the cooling efficiency can be increased by adding atomized water. The added water flow usually is dosed based upon the ash flow and temperature so as to guarantee the full evaporation of the injected water in order to obtain at the exhaust, if necessary, dry ash suitable to be ground and transported pneumatically so as to be mixed to lighter ashes.

FIELD OF THE INVENTION

The present invention relates to a system and a method for extracting, cooling and recovering energy for large quantities of heavy ashes produced by solid fuel boilers.

BACKGROUND OF THE INVENTION

The constant growth in the request for solid fossil fuels for the production of electric energy makes more frequent the combustion also of coals and lignites with high ash content. The combustion of the latter in high-power boilers involves a considerable production of heavy ashes, even up to 100 tons/hour, often containing high percentages of unburnt matters. The dry cooling or mainly dry cooling of such quantities requires large quantities of cooling air, even twice or thee times greater than the fossil fuels with high calorific value.

As illustrated in EP 0 471 055 B1, in some known ash extraction and dry cooling systems, cooling air, once heated due to the thermal exchange with the latter, is introduced into the boiler from the bottom thereof. Therefore, at first the greater is the quantity of the produced ash, the greater is the heat recovery which is supplied in the boiler by the cooling air in the above-mentioned way, both for the thermal exchange with the air and for the combustion of the unburnt matters.

However, in order to avoid that the combustion efficiency be influenced negatively by the air introduced into the combustion chamber from the bottom rather than from the burners or from other specific air entrances and/or in order to avoid similar unwished effects on the production of nitrogen oxides (NO_(x)), the boiler designers prefer limiting this quantity to a maximum value of 1.0-1.5% of the total combustion air.

For what just illustrated, the known cooling systems do not succeed in implementing, in an efficient and effective way, the dry cooling or mainly dry cooling of the heavy ashes and the disposal of the related cooling air, above all if such ashes are in large quantities, with high content of unburnt matters and therefore at high temperature. In particular, even when such cooling, recovery of the thermal energy and disposal are succeeded to be obtained, they are achieved with considerable plant complications and with consequent very high implementation and handling costs.

Therefore, the technical problem underlying and solved by the present invention is to provide a system and method for the extraction and cooling of heavy ashes coming from a solid fuel combustion chamber which allow obviating to the drawbacks just mentioned with reference to the known art.

SUMMARY OF THE INVENTION

The above-mentioned problem is solved by a system according to claim 1 and by a method according to claim 46.

Preferred features of the present invention are present in the claims depending from the invention itself.

The present invention provides some important advantages which will be appreciated in full in the light of the detailed description reported hereinafter.

The main advantage consists in that the present invention allows to carry out an adequate, effective and efficient dry cooling or mainly dry cooling of the ashes without exceeding the above-mentioned limit of 1.0-1.5% for the cooling air introduced into the combustion chamber from the bottom. Such advantage is particularly important in the above-mentioned case of coals with high content of heavy ashes. This is mainly obtained by separating the whole extraction and transport system into two environments with different atmospheric pressure, the first one connected to the combustion chamber and the second one to the economizers' area. Such separation, among other things, allows sending to the latter area some air exceeding the above-mentioned 1.5% and the possible steam contained therein.

Based upon a preferred and particularly advantageous embodiment, said environment separation is implemented by means of a head of the same transported ash and therefore substantially without the need of additional devices for the system. This allows obtaining the above-mentioned effective cooling also of large flows of ashes with high temperature by keeping, however, an extreme construction and operation simplicity of the system itself, to the advantage of the implementation, handling and maintenance costs. Based upon such preferred embodiment, the invention substantially allows to optimize the system described in EP 0 471 055 B1 by widening the potentiality of applications thereof to large flows of heavy ashes coming from coals or lignites with high ash content.

Upon summarizing the detailed description of preferred embodiments reported hereinafter, the present invention relates to an extraction and air/water cooling system for large flows of heavy ashes, produced by solid fuel boilers, able to reduce the final temperature of the extracted ash, without increasing the air quantity entering the boiler throat, usually fixed by the boiler designers at a value around 1.5% of the total combustion air. When the air quantity necessary for cooling process exceeds the maximum quantity which can be admitted into the boiler, the system allows exceeding air to be sent to the fume duct in the most proper point thanks to a separation of the cooling environments made by the ash itself.

The separation of the environments of the cooling system is automatically handled by the system upon ash and/or flow measurement performed at the exhast. If the cooling air is not sufficient to cool the ash, the cooling effectiveness can be increased by adding atomized water. The added water amount usually is dosed based upon the ash flow and temperature so as to guarantee the full evaporation of the injected water to obtain if necessary, at the exhaust, dry ash, suitable to be ground and transported pneumatically. The water has the great advantage, with respect to air, to allow an effective cooling of the ash itself with considerable lower weight quantities (in a ratio around 1:100 under the working conditions which are considered in this case) and it allows then a drastic reduction of the air quantity to be sent to the fume duct. This allows reducing the negative impact, until making it practically negligible, that an increase in the quantity of the fumes involves for the possible oversize of the apparatuses and the increase in the energy necessary for treating the fumes themselves until the ejection from the chimney.

The proposed system, upon use, is mainly constituted by:

-   -   1. a transition hopper between boiler and extractor, the latter         of the type subject of the already mentioned patent EP 0 471 055         B1;     -   2. the above-mentioned extractor;     -   3. an ash crusher;     -   4. a transition storage reservoir between the crusher and a         conveyor-cooler, such storage reservoir being for example in the         form of hopper;     -   5. the above-mentioned conveyor-cooler, equipped with suitable         ploughshares entrusted with the function of mixing the ash onto         the conveyor itself and with nozzles for water injection;     -   6. a pipeline, or duct, for the connection between the         conveyor-cooler (in the area of the discharge hood of the         latter) and the most suitable point of the system for treating         boiler fumes (usual upstream of the electro-filter that is of         the air/fume exchanger, but the choice could modify depending         upon the fume line composition, such as presence or absence of         DeNOx and/or DeSOx systems and related configuration) for the         outlet of the cooling air exceeding the maximum acceptable by         the boiler;     -   7. a final discharge apparatus, able to allow the discharge of         the ash by preventing at the same time the entrance of         uncontrolled air into the system (for example a valve or a         vibrating extractor or simply a closed connection with other         transport or storage closed apparatus);     -   8. an ash-water mixer which will be activated, as alternative to         the final discharge apparatus of the previous item 7., thanks to         the drive of a flow diverter, in case the system, due to the         anomalous condition of the ashes (high quantity and/or         temperature) is no more able to guarantee an adequate cooling of         the ash—such mixer, in turn, will be equipped with:         -   a connecting pipeline, or duct, for the outlet of the humid             air to the pipeline of item 6., and         -   a final discharge apparatus equivalent to the one described             in item 7., able to allow the ash discharge from the system             by preventing at the same time the re-entering of the outer             air;     -   9. a regulation and control system, able to guarantee the         automatic carrying out of the operations as it will be described         hereinafter in the operation description part.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages, features and application modes of the present invention will be evident from the following detailed description of some preferred embodiments, shown by way of example and not for limitative purposes. The figures of the enclosed drawings will be referred to, wherein:

FIG. 1 shows a general layout exemplifying a preferred embodiment of the invention system, in an operation mode which provides a pressure separation between two cooling environments;

FIG. 2 shows a schematic longitudinal-sectional view of a separation area of the two cooling environments of the system of FIG. 1;

FIG. 3 shows a cross-sectional view taken according to the line A-A of FIG. 2;

FIG. 4 shows a general layout exemplifying the system of FIG. 1, in a different operation mode which does not provide said separation into two cooling environments;

FIG. 5 shows a cross-sectional view of a continuous mixer with double shaft equipped with nozzles for the cooling water of the system of FIG. 1, taken along the line B-B of this last figure; and

FIG. 6 shows a general layout exemplifying the system of FIG. 1, in an operation mode which provides to send the still hot ash to the mixer of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

By firstly referring to FIG. 1, a system for extracting and cooling combustion residues, of the type used for example in solid fossil fuel thermo-electric plants and according to a preferred embodiment of the invention is designated as a whole with 1. As it will be better appreciated hereinafter in the description, the system 1 is particularly suitable to handle large flows of heavy ashes, produced, for example, by the combustion of coals or lignites with high content of ashes.

For greater illustration clarity, the different components of the system 1 will be described hereinafter by referring to the path followed by the combustion residues from the extraction thereof from the bottom of the combustion chamber (or boiler), designated with 100, to the disposal thereof.

Immediately downstream of the combustion chamber 100, or better a transition hopper 105 thereof, the system. 1 provides a first extraction and/or transport unit, in particular a dry extractor 9 mainly made of steel with high thermal resistance. Such extractor 9 is of the kind known on itself and described for example in EP 0 252 967, herein incorporated by means of this reference. The extractor 9 gathers the heavy ashes which precipitate downwards into the combustion chamber 100 through the transition hopper 105 mentioned above.

The extractor 9, at the side walls of its own casing, has a plurality of entrance holes for the outer cooling air, distributed in a substantially regular way along the development of the extractor 9 itself and each one designated with 10. Such entrances 10 can be equipped with means for adjusting the quantity or can be made active or deactivated. Furthermore, the extractor 9 has an additional entrance for the outer cooling air 19, preferably adjusted too by an automatic valve or by equivalent adjusting means of the flow and arranged substantially at an ending portion of the extractor 9 itself.

Cooling air is sucked through the entrances 10 and 19 within the extractor 9 and in countercurrent with respect to tranported ashes by the effect of the depression existing in the combustion chamber 100. More in detail, air enters because of the depression existing in the transition hopper 105, on the bottom thereof there is a depression adjusted by the control system of the combustion chamber 100 (generally around 300-500 Pa under the atmospheric pressure).

Downstream of the extractor 9 the ashes are fed to a breaker or crusher 3, which crushes the coarsest fractions thereof so as to increase the thermal exchange surface and thus to improve the effectiveness of such exchange and thus cooling process.

Downstream the crusher 3 an additional entrance for the outer cooling air is provided, designated with 17 and in case equipped, with means for flow regulation, as those already described. Also in this case, the air coming from the entrance 17 is fed in countercurrent through the crusher 3 itself and along the first extractor 9 by the effect of the depression existing in the combustion chamber 100. Such cooling air results useful not only for cooling the ash but also for cooling the machines.

As illustrated in greater detail in FIGS. 2 and 3, downstream of the crusher 3 the ashes are conveyed by means of a hopper/reservoir 8 to a second steel-belt conveyor-cooler 6. As it will be illustrated in greater detail hereinafter, under determined conditions the described system configuration allows the hopper 8 to operate like a storage reservoir, by allowing to accumulate ash so as to guarantee the disconnection of the two atmospheres from the extractor 9 and of the conveyor-cooler 6. In particular, in presence of such accumulation, the conveyor 6 operates exactly as second extractor, by operating continuously under a material head which guarantees the separation between the environment of the extractor associated to the pressure of the combustion chamber 100 and the one of the conveyor/cooler associated to the different pressure of the economizers' area.

Sensors with maximum and minimum level, designated with 7, and a layer leveller 18, the latter arranged at an initial portion of the entrance of the conveyor 6, are associated to the hopper 8.

The position indicated by the layer regulator 18 connected to the value of the velocity of the belt of the conveyor cooler 6 provides information about the ash volumetric flow, useful along with the temperature measurement in order to regulate cooling fluids.

Onto the conveyor 6 the ash continues to be cooled both by means of air resucked from outside through additional entrances 11 arranged onto the side walls of the extractor 6 itself in a way analogous to what already illustrated for the first extractor 9, both, when needed, by means of water finely dosed by means of additional dispensing nozzles 12 positioned inside the covering of the conveyor 6.

At this point it will be understood then that the system 1 is equipped with an air/water cooling system, implemented among other things by the air entrances 10, 11, 17 and 19 and by the water delivery nozzles 12.

The system 1 further provides means for feeding the cooling air, heated after the heat exchange with the combustion residues, in a fume duct 101 associated to the combustion chamber 100. In the present embodiment such feeding means comprises a duct 4, properly insulated and thermally traced to avoid condensates, apt to be selectively adjusted and however interdicted/enabled by means of an automatic valve 15 (or equivalent means) arranged along the development thereof.

More in detail, the duct 4 connects, or better is apt to connect, the discharge area of the conveyor 6 and/or incase of the mixer 2 to said economizers' area, under negative pressure too. Preferably, the duct 4 flows upstream of an air/fume exchanger 102 (fume side) apt to pre-heat the combustion air and typically provided in the combustion systems associated to the invention. Such exchanger 102 can be of the type commonly called Ljungstrom.

The ash cooling onto the conveyor 6 is made more effective thanks to the presence of specific mixing means, in particular substantially wedge-shaped members 14 fixed with respect to the conveyor belt 6 itself and which in the present example have a shape like a ploughshare. Such ploughshare-like members 14 are distributed in a substantially regular way along the development of the conveyor 6 and arranged at the ash transport section. As mentioned above, the ploughshare-like members 14 plough the ashes by operating a continuous mixing during the transport onto the belt, by exposing in this way the maximum surface available for the thermal exchange with the cooling air and/or water.

Downstream of the conveyor 6 an automatic deviating valve 16 (or equivalent means for selectively deviating the ash flow) is provided, which allows to feed selectively the cooled ash to discharge means 13 directed outside or to a continuous mixer 2, in the present example in communication with the outside too and shown in greater detail in FIG. 5. The discharge conveyor 13 is equipped with a device for controlling the entering air, not illustrated, to eliminate the uncontrolled entrance of air from outside (or, in embodiment variants, to connect the system to other transport or storage closed environments).

The mixer with water 2 allows completing the cooling of the ash if necessary to reach temperature values compatible with the downstream processes or to humidify the ash to reduce the dust emission under certain transport and disposal conditions. The mixer 2 is equipped with a discharge hood 21, equipped with means able to allow the ash discharge from the system by preventing at the same time an uncontrolled re-entering of the outside air. Such device can be constituted for example by a valve with double clapet or by rubber flushes which, by deforming under the ash weight, allow the discharge thereof into the minimum required passage section.

Based upon a preferred embodiment, a pipeline for connecting the mixer 2 to the duct 4 is provided for the outlet of the air and steam in the latter.

The system 1 then comprises means for sensing the temperature and/or volumetric and/or ponderal quantity of the ashes, which in the present example are arranged at the ending portion or at the discharge portion of the conveyor 6 and/or on the main extractor 9 or more preferably at the ash exhaust at the conveyor 13. Advantageously, sensors of the above-mentioned type are provided also at the hopper/reservoir 8.

Still at such hopper 8, load cells or equivalent means can be provided to control the ash level in the hopper/reservoir.

Furthermore, temperature sensor means arranged at the duct 4 can be provided.

The system 1 comprises a control system, in communication with said sensor means, apt to control the operation modes of the system 1 in relation to the ash flow and temperature.

The operation modes of the system 1, and in particular those of the cooling system thereof controlled by the control means described above, will be now illustrated in greater detail.

First of all, the ash temperature and/or flow values provided by the sensor means are compared by the control system to pre-fixed and stored values, and based upon the result of such comparison the operation mode most suitable to the operation of the system 1 is determined. Regarding the need for carrying out measurements of temperature and/or flow, it is to be noted that the ash temperature increase usually is linked to the increase in the flow thereof in the here considered system 1.

The system in the starting phase is configured in the mode illustrated in FIG. 4, by adjusting all air entrance valves 10, 11, 17 and 19 and by closing the automatic valve 15, so as to obtain that the whole air quantity corresponding to 1.5% of the combustion air be sucked through the bottom throat of the hopper 105 of the boiler 100 by crossing in countercurrent the ash both in the extractor 9 and in the conveyor 6.

Such operative mode is followed until the ash temperature at the exhaust of the conveyor 6 reaches the predetermined value T_(minimum).

In such operative mode control means act onto the relative velocity of the belt of the extractor 9 and of the belt of the conveyor 6, substantially making so that the conveyor 6 have an ash potential flow greater than the extractor 9 in order to avoid the formation of a material head within the hopper 8.

When the value T_(minimum) is exceeded, the system acts onto the velocity of the conveyor 6, in particular by reducing and adjusting it so as to determine an ash accumulation in the hopper 8 and then to create a continuous ash plug and furthermore it opens the valve 15 of the duct 4 so as to create two different atmospheres respectively in the extractor 9 and in the conveyor 6, the first one connected to the pressure existing in the boiler and the second one connected to the pressure existing in the fume duct.

In such operative mode the air valve entrances 10, 19 and 17 of the extractor 9 and of the hopper 8 are automatically adjusted so as to concentrate in the extractor only the whole 1.5% of cooling air which can be introduced into the boiler. Also the valves 11 and in case subsequently the nozzles 12 of the conveyor 6 are regulated by adding at first air until a percentage calculated so as not to influence on the systems for treating the fume downstream and subsequently water if necessary to reach the wished cooling.

In such configuration of environment separation, the cooling air acting on the main extractor 9 introduced by means of the entrances 10, 17 and 19 crosses such extractor in countercurrent and enters the combustion chamber 100 in the limit of 1.5%. The cooling air exceeding 1.5% is taken from outside through the entrances 11 of the conveyor 6, it crosses the latter in equicurrent and it is sucked through the duct 4, together with the steam produced by the possible water local cooling, by the depression existing in the economizers' area.

In such way the maximum possible combustion of the possible unburnt matters is obtained onto the belt of the extractor 9 by bringing the related energy back to the boiler and by adding water onto the belt of the conveyor 6 an effective cooling is obtained without requesting therefor a greater energy consumption by the system for treating the fumes, consequently increasing the performance of the steam generator.

Such operative modes are exemplified in FIG. 1.

In presence of the ash head mentioned above, the emptying of the load hopper 8 is avoided by controlling the velocity of the conveyor 6 depending upon the detections of the sensors of maximum and minimum level 7. In particular, if the level reaches the minimum one the slowing is provided until stopping the conveyor 6, whereas when the minimum level is exceeded the re-starting of the conveyor 6 is provided and upon reaching the maximum level the increase in the speed and then in the quantity of the belt of the conveyor 6 is provided.

In the here considered configuration, the control means can make use of additional information detected by specific sensor means, related in particular to the ash temperature in the hopper 8 and to the feeding speed of the conveyor 6. The latter, combined with the (fixed) value of the extraction section defines exactly the ash volumetric flow. It is clarified that the extraction level, in order to avoid possible problems in the extraction section itself, will have to be greater by a suitable margin in the size of the ash pieces outgoing from the crusher 3.

Furthermore, in an additional operative mode exemplified in FIG. 6, the system 1 can be handled also in case of very high ash flows/temperatures—even higher than the design values—for example depending upon the kind of fuel or upon cleaning operations of the combustion chamber 100. In such case, wherein the ash temperature is supposed to be higher than the value T_(very high), the system 1 provides an operative mode like the last described and the discharge of the still hot ash to the mixer 2 instead of to the conveyor 13 by means of the deviating valve 16.

In mixer 2 an additional water flow could be introduced so as to bring the ash to the provided final temperature (typically indicatively 80° C.) with a proper humidity content (preferably around 10%) to guarantee the dust absence in the subsequent motion operations.

In order to avoid that the steam generated by such cooling in the mixer 2 rises back towards the conveyor 6 (with the risk of generating condensate), an upside-down-“Y”-like connection can be provided directly between the conveyor 6, the mixer 2 and the duct 4. Thanks to such configuration, the air and in case the steam arriving from the conveyor-cooler 6 goes towards the connecting duct with the fume line by joining the steam generated in mixer 2. The condensate risk remains in this connecting duct (between the mixer 2 and the main duct 4), which could be properly heated whenever the design conditions had identified danger of condensate formation and related ash incrustations.

It will be understood that said prefixed values of temperature and/or flow and of predetermined amount of combustion air can be selectively set by an operator managing the system 1.

Furthermore, it will be understood that the previously described operative modes are only one of the possibility for managing the system 1. A simpler operative mode, for example, can provide that the ash head be created upon reaching a prefixed temperature value, while system managing, occurring for the remaining part, will properly modulate flows of cooling air and water, the latter if necessary.

A series of operative modes like the ones considered so far can be set manually or automatically by means of a managing and control system which, based upon the ash temperature/flow value, determines cooling mode of the ash itself by acting on the formation of the separation area, on the air—flows entering the extractor 9 and the conveyor 6, on the possible dosage/usage of atomized water and on the activation of the deviating valve.

Generally, it will be appreciated at this point that the system 1 has a total operative versatility and therefore the capability of managing practically any ash quantity, and this without problems associated to the introduction of an excessive flow of cooling air from the bottom of the boiler 100. As mentioned above, such versatility is obtained by allowing the introduction of even very high cooling air flows and by feeding the additional air flow (which is not right to introduce from the boiler bottom in the fume duct) and by means of the possibility of adding, needed, also cooling water.

As far as this last aspect is concerned, preferably the system 1, through its control means, can dose adequately the used water quantity so that it vaporizes completely during cooling process and that, upon outgoing from the conveyor 6, substantially dry ashes are then obtained suitable to be ground and transported pneumatically. This can be obtained by keeping ash final temperature above 100° C. The water quantity to be atomized and injected will be controlled by means of a thermal balance which causes on one side the heat to be removed from the ash (quantity product for the variation in the specific enthalpy requested between the temperature in the hopper 8 and the discharge final temperature) and on the other side the sum of the water vaporization heat and the enthalpy variation subjected by the cooling air to be equal.

Furthermore, it will be appreciated that sending part of the cooling air to the fume duct upstream of the air/fume exchanger allows an optimum heat recovery, by allowing to emphasize the performance advantages already associated to the dry extractors used in this case and described in the already mentioned patent EP 0 471 055 B1.

It will be also appreciated that the presence of the ploughshare-like members or means equivalent thereto, also together with the possibility of activating selectively the water cooling by means of the nozzles 12, allows levelling ash temperature.

Furthermore, it will be appreciated that the temperature sensors arranged at the duct 4, apart from allowing a more complete control of the system parameters, also allow to verify the formation of possible condensation points at the whole duct 4 due to the steam deriving from the cooling water. In fact, knowing both the temperature of the air itself and of the atomized water quantity allows easily to calculate the humidity related to the cooling air and to verify that:

-   -   on one side the humidity itself is below 100% with proper         important margin; and     -   on the other side, also in possible cold points existing in the         path (and that is mainly on the covering of the conveyor 6 and         on the surface of the connecting duct 4) the water content in         the air is not as to generate condensate startings, which could         result to be troublesome for the good system operation.

In order to avoid any risk of condensate formation in the system, an additional connecting duct (or equivalent means) can be provided between the transition hopper 105 and the conveyor 6 near the hopper 8, by moving selectively the entrance of the outer air on such duct and providing regulation valves of the quantity both of the hot air coming from the transition hopper 105 and of the cold environment air. This allows raising the air temperature in the system to such levels so as to eliminate the risk of condensate formation. The above-mentioned adjustment of the entering hot and cold air flows could be then take place based upon the detections of the above-mentioned temperature sensor positioned on the duct 4.

At last it will be understood that the above-mentioned separation in two environments can be obtained also by means of devices different from those described above. For example, between the extractor 9 and the conveyor 6 additional devices such as clapet-like valves or equivalent devices can be provided, again the separation of the two environments can be obtained by applying under the hopper/reservoir 8 a second crushing stage with variable quantity with respect to the crusher 3, so as to generate in the hopper the necessary ash head apt to separate the environments.

It will be appreciated that the invention allows an effective recovery of the energy deriving from having sent the maximum quantity of outer air on the extractor 9 and from having reduced drastically the air quantity on the second extractor 6 (for the water addition) and therefore the energy necessary for the fume treatment.

The invention has also as object a method for extracting and recovering energy of heavy ashes as described so far with reference to the system 1.

The present invention has been so far described by referring to preferred embodiments. It is to be meant that other embodiments belonging to the same inventive core may exist, all comprised within the protective scope of the herebelow reported claims. 

1. A system for extracting, cooling and recovering energy of heavy ashes adapted to be used in association with a combustion chamber, the system comprising: (a) extraction and transport means for extracting and transporting heavy ashes coming from the combustion chamber; (b) a cooling system for cooling the heavy ashes, located at said extraction and transport means and adapted to determine a feeding of cooling air at the extraction and transport means, wherein at least a portion of said cooling air is introduced into the combustion chamber from the bottom thereof; (c) pressure insulation means adapted to determine a separation of the atmospheres between a first environment and a second environment of said extraction and transport means, said first environment being connected to the atmosphere of the combustion chamber and said second environment being connectable connected to the fume duct; and (d) control means, adapted to determine activation of said pressure insulation of environments depending upon ash temperature and/or flow.
 2. The system according to claim 1, wherein said cooling system is a twofold air-water cooling system and said water cooling is activatable at said second environment. 3.-6. (canceled)
 7. The system according to claim 1, wherein, under condition of pressure separation of environments, said cooling system is adapted to determine a feeding of cooling air in countercurrent with a flow of heavy ashes in said first environment and in equicurrent with said flow in said second environment. 8.-14. (canceled)
 15. The system according to claim 1, wherein said control means is adapted to determine said separation of environments so that cooling air flow, entering the combustion chamber from the bottom, does not exceed a predetermined amount of total combustion air.
 16. The system according to claim 15, wherein said predetermined amount is equal to about 1.0-1.5%.
 17. The system according to claim 1, further comprising feeding means for feeding cooling air and a possible steam deriving from the cooling water into a combustion fume duct associated with the combustion chamber, wherein said feeding means are adapted to connect the combustion chamber with the second environment, substantially downstream of the cooling process.
 18. (canceled)
 19. The system according to claim 17, wherein said feeding means reach said fume duct at an economizers' area.
 20. The system according to claim 17, wherein said feeding means for feeding cooling air into the fume duct outlet upstream of an air/fume exchanger adapted to pre-heat combustion air.
 21. (canceled)
 22. The system according to claim 17, wherein said pressure insulation means comprise interdicting or enabling means for interdicting or enabling said feeding means for feeding into the fume duct, the interdicting or enabling means being controlled by said control means in order to determine said environment separation when needed. 23.-24. (canceled)
 25. The system according to claim 1, wherein said extraction and transport means comprise a first extraction unit adapted to be located immediately downstream of the combustion chamber, and a second transport unit located downstream of said first unit, wherein said pressure insulation means are adapted to produce a pressure separation between said first extraction unit and said second transport unit. 26.-27. (canceled)
 28. The system according to claim 1, wherein said pressure insulation means comprise means adapted to create a head of heavy ashes between said two environments, adapted to determine said pressure separation thereof.
 29. The system according to claim 28, wherein said pressure insulation means comprise a storage reservoir means adapted to receive heavy ashes creating said head.
 30. The system according to claim 29, wherein said pressure insulation means comprise a hopper adapted to receive heavy ashes creating said head.
 31. The system according to claim 28, wherein said control means comprise one or more level sensors arranged at said head.
 32. The system according to claim 1, further comprising a crusher of heavy ashes, located at said extraction and transport means.
 33. (canceled)
 34. The system according to claim 28, wherein said means, adapted to create an insulation head, are adapted to determine formation of said head immediately downstream of a crusher of heavy ashes, located at said extraction and transport means. 35.-44. (canceled)
 45. The system according to claim 1, further comprising a duct for feeding hot air from said combustion chamber to a unit of said extraction and transport means contained in said second environment.
 46. A method for extracting and cooling heavy ashes coming from a combustion chamber, the method comprising: (a) extracting the heavy ashes from the combustion chamber; (b) cooling the heavy ashes along an extraction and transport path by feeding cooling air along the path, introducing, downstream of a cooling process, at least part of said air into the combustion chamber from the bottom thereof; and (c) depending upon temperature and/or flow of the heavy ashes, selectively activating a pressure insulation between a first environment and a second environment located along said extraction and transport path, said first environment being located immediately downstream of the combustion chamber and said second environment being located downstream of said first environment.
 47. The method according to claim 46, wherein said cooling (b) is a twofold air-water cooling and said cooling (b) provides activation of water cooling depending upon temperature and/or quantity of the heavy ashes.
 48. (canceled)
 49. The method according to claim 47, wherein said cooling (b) provides regulation of cooling water dispensing so that the cooling water wholly vaporizes during the cooling process, and substantially dray ashes are obtained at the exhaust of said extraction and transport path.
 50. The method according to claim 47, wherein said cooling (b) provides an activation of the water cooling at said second environment.
 51. (canceled)
 52. The method according to claim 46, wherein said cooling (b) provides, under said condition of pressure separation of environments, a feeding of cooling air in countercurrent with a flow of heavy ashes in said first environment and in equicurrent with said flow in said second environment. 53.-57. (canceled)
 58. The method according to claim 46, wherein said activating (c) provides that said environment separation is carried out so that cooling air flow entering the combustion chamber from the bottom does not exceed a predetermined amount of total combustion air.
 59. The method according to claim 58, wherein said predetermined amount is equal to about 1.0-1.5%.
 60. The method according to claim 46, further comprising providing a feeding of cooling air and possible steam deriving from the cooling water into a combustion fume duct associated with the combustion chamber, wherein said feeding into the fume duct takes place starting from said second environment, substantially downstream of the cooling process.
 61. (canceled)
 62. The method according to claim 60, wherein said feeding into the fume duct provides an outflow in the latter at an economizers' area.
 63. The method according to claim 60, wherein said feeding into the fume duct provides an outflow into the fume duct upstream of an air/fume exchanger adapted to to pre-heat the combustion air.
 64. (canceled)
 65. The method according to claim 60, wherein said activating (c) provides that said pressure insulation be obtained through interdiction or enabling of said feeding of cooling air into the fume duct.
 66. (canceled)
 67. The method according to claim 46, wherein said extraction and transport path comprises a first extraction portion arranged immediately downstream of the combustion chamber and a second transport portion arranged downstream of said first portion and wherein said activating (c) provides that said pressure insulation is obtained between said first extraction portion and said second transport portion. 68.-69. (canceled)
 70. The method according to claim 46, wherein said cooling (c) provides the creation of a head of heavy ashes between said two environments, adapted to determine said pressure separation thereof.
 71. The method according to claim 70, wherein said cooling (c) provides level detection of said head.
 72. The method according to claim 46, further comprising providing a crushing of heavy ashes, performed within said extraction and transport path.
 73. The method according to claim 72, wherein said crushing is performed between said first environment and said second environment. 74.-80. (canceled)
 81. The method according to claim 46, further comprising providing a feeding of hot air from the combustion chamber to a portion of said extraction and transport path contained in said second environment. 